The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to guiding the dispersion of inflation gas during inflation of the bolster.
An active bolster is a type of vehicle occupant protection device having a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deploying air bag cushions through various openings, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. Co-pending application publication US2011/0316300A1, filed Jun. 26, 2010, entitled “Active Knee Bolster for Automotive Vehicle,” which is incorporated herein by reference in its entirety, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. Active bolsters are also commonly integrated into door panels for side impact protection.
In a typical structure, an active bolster includes a bladder comprised of an outer or front wall that faces a vehicle occupant attached to an inner or back wall along a sealed periphery. One or both of the walls are deformable in order to provide an inflatable bladder. The walls are initially spaced apart by only a small amount when in their non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The inner and outer walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They can be blow molded or injection molded. The inner wall commonly employs a pleated structure that unfolds in an accordion-like fashion during inflation to provide the increasing volume of the bladder for forming an impact cushion. A central portion of the inner wall is braced against a reaction surface such as a structural frame or strut of the vehicle.
The pressurized gas needed for inflating an active bolster during a crash event is supplied by an inflator. The inflator includes a canister containing a pyrotechnic material and other substances to quickly generate a large amount of expanding gas when triggered. The gas is discharged through a nozzle into the bladder. A bay or recess is typically provided in the inner wall to accommodate the inflator. One reason for placing the nozzle within the bladder has been to directly couple the inflation gas to the bladder, thereby avoiding any need for ducts or other means for conveying the gas.
Since inflation must occur very quickly, the discharged gas is at a high pressure. The resulting structural load applied to the plastic bladder walls just at the areas being directly impacted by the gas is high enough to cause extra stretching of those areas. The localized stresses create corresponding bulges in the walls which result in uneven deployment, loss of energy, and potential rupturing. Loss of energy may require a larger, more expensive inflator to be used. To combat these problems, a deflecting cap could be mounted onto the nozzle to diffuse the discharging gas, but the manufacturing cost and assembly operations required would negatively impact the overall cost of the bolster.